Secondary batteries are widely used as power supplies of mobile devices and backup power supplies. However, the secondary batteries are deteriorated by repeated charge and discharge, use at high temperature, overcharge and overdischarge. In the case of such deterioration of a secondary battery, problems such as the shortening of usable time and inability to do a necessary backup occur, wherefore it is important to judge the deterioration of the secondary battery.
A method for measuring a voltage drop for a current value at the time of discharge and calculating internal resistance of the secondary battery to judge a deteriorated state (see, for example, patent literature 1) and other methods have been proposed as secondary battery deterioration judging methods.
However, in the case of a backup power supply or the like, if deterioration is judged when the discharge is started as in patent literature 1, a sufficient discharge capacity cannot be obtained already at that point of time and the occurrence of a problem such as the shortage of a backup time cannot be avoided. Accordingly, measures such as the implementation of maintenance to perform discharge for regular deterioration judgments are necessary. Since the power supply cannot be backed up during the implementation of the maintenance to perform discharge for the deterioration judgment, there are problems such as the necessity to stop a backup function.
Patent Literature 1:
    Japanese Unexamined Patent Publication No. 2003-243042